bpo-32797: linecache should search for sources if loader doesn't find them #6653
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Looks good to me in relation to my comments on python-list, that this is what the docs say. But I haven't reviewed bpo-32797, so I'm not going to approve this without @embray's feedback. Further discussion should really be on the issue tracker, so I'll add any other comments I have there. |
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LGTM. I don't know exactly what would be impacted by this if the source code search falls through for normal extension modules, but regardless the current behavior is a regression. |
sageb0t
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Jun 17, 2018
I've been getting to the bottom of why tracebacks aren't displaying Cython sources on Python 3. The problem turns out to be multi-faceted, and fixing it right would also mean fixing some things in general, since the way it works now is a hack. Basically, the only reason it works at all on Python 2, is that the `linecache` module on Python 2 has some code which, given a relative filename (with an extension unrecognized by the import system) like `sage/rings/integer.pyx`, it will search for this file under all `sys.path` entries and, if found, read the source lines from that file. This, in turn, only works for Sage because we actually install the `.pyx` sources in the sage package. This does not work in Python 3. In `linecache.updatecache`, before it tries the `sys.path` search, it checks if the module object has a `__loader__`, and calls its `get_source()` method if it exists. On Python 2 this isn't a problem since modules don't necessarily have a `__loader__`, and in particular extension modules don't. But on the reworked import system in Python 3, pretty much every module has a `__loader__`--in the case of extension modules an `ExtensionFileLoader`. But the built-in `ExtensionFileLoader` of course knows nothing about Cython so its `get_source()` method just returns `None`. `linecache.updatecache` assumes this is correct (why would the loader lie?) and returns. The simplest way to fix this is to remove the `get_source()` method from the `ExtensionFileLoader` class. This way, Python 3 works the same way as Python 2. '''Upstream''': - https://bugs.python.org/issue32797 - python/cpython#6653 URL: https://trac.sagemath.org/24681 Reported by: embray Ticket author(s): Jeroen Demeyer, Erik Bray Reviewer(s): Frédéric Chapoton
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@pfmoore: Erik Bray commented positively on this PR, so can this be approved then? |
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https://bugs.python.org/issue32797